甲苯与氯原子光氧化产生二次有机气溶胶粒子实时探测研究

在烟雾腔内,用紫外光照射甲苯、氯气、一氧化氮和空气的混合物,启动甲苯和氯原子的光氧化反应和一系列的后续反应,产生非挥发性和半挥发性有机化合物.半挥发性有机化合物可以在气态和粒子态之间进行分配,产生二次有机气溶胶粒子.用实验室自制的气溶胶飞行时间质谱仪实时测量这些粒子产物的分子成分和粒径分布,并初步探讨了这些组分的可能反应机理.     

二次有机气溶胶中二羰基化合物的研究进展

二次有机气溶胶的形成是大气环境化学的研究热点。二羰基化合物对二次有机气溶胶形成具有重要的研究意义。由于二羰基化合物在液相中发生聚合反应,在液相中的分配大于Henry定律的预测值,影响二次有机气溶胶的形成。通过二羰基化合物乙二醛和甲基乙二醛在大气中光氧化和异相反应的研究,评述了二羰基化合物对二次有机气溶胶形成的研究发展。     

气溶胶飞行时间质谱仪分析间-二甲苯光氧化颗粒相产物

在自制的烟雾腔内,用紫外光照射间-二甲苯、亚硝酸甲酯、一氧化氮和清洁空气的混合物,可以启动间-二甲苯和羟基自由基(OH)的光氧化反应和一系列的后续反应,产生非挥发性和半挥发性有机化合物.半挥发性有机化合物可以在气态和粒子态之间进行分配,产生二次有机气溶胶粒子.采用实时测量气溶胶粒子粒径大小和化学成分的气溶胶飞行时间质谱仪快速、实时地测量了这些粒子的尺度、它们的分子成分和粒径分布.通过化学分析,得到酚、醛、酮和羧酸等重要的间-二甲苯光氧化产物,为讨论间-二甲苯光氧化反应机理提供了新的信息.     

温湿度对EBM气溶胶灭火剂吸湿的影响

EBM气溶胶灭火剂是一种新型高效灭火剂,其灭火效率高于哈龙类灭火剂.燃烧反应产生的白色烟雾对火灾具有抑制作用.白色烟雾中含有固体颗粒物质,这些颗粒物降落形成残留物湿后的残留物对金属材料及线路板等有腐蚀性.研究了温湿度对气溶胶灭火剂吸湿的影响.研究结果表明:空气的相对湿度是影响气溶胶颗粒物吸湿的主要因素.     

EBM气溶胶灭火剂产物的潮解研究

EBM气溶胶灭火剂是一种新型高效灭火剂,其灭火效率高于哈龙类灭火剂。燃烧反应产生的白色烟雾对火灾具有抑制作用。白色烟雾中含有固体颗粒物质,这些颗粒物降落形成的残留物潮解后对金属材料及线路板等有腐蚀性。对气溶胶灭火剂颗粒物潮解进行研究,研究结果表明:空气的相对湿度是影响气溶胶颗粒物潮解的主要因素。     

湿式氨法烟气脱硫中气溶胶的形成特性研究

气溶胶的形成是湿式氨法烟气脱硫过程存在的主要问题,通过测试分析氨法脱硫前后细颗粒的浓度与粒径分布、颗粒形态及其组成的变化特性,探讨了氨法脱硫中气溶胶的形成机理,并考察了影响气溶胶颗粒形成的主要因素。结果表明:氨水挥发逸出的气态NH3与烟气中SO2发生气相反应是气溶胶形成的主要原因,气溶胶含(NH4)2SO4、(NH4)2SO3、NH4HSO3等组分,粒径集中在0.07～0.70μm范围内,氨法脱硫系统对其难以有效脱除;氨水脱硫液温度及其浓度、烟气中SO2浓度、液气比等对气溶胶形成具有重要影响,形成量随氨水脱硫液及烟气中SO2浓度升高而增多,在保持NH3:SO2化学计量比不变的情况下,随液气比增大,气溶胶颗粒形成量减少。最后,对气溶胶颗粒的控制措施提出了建议。     

不同源挥发性有机物生成二次有机气溶胶的研究进展

总结了近几年典型VOCs氧化生成二次有机气溶胶(SOA)的影响因子(大气氧化剂、湿度及种子气溶胶等),从生物源和人为源2个方面,总结了单萜烯类、异戊二烯、芳香烃及小分子有机物等转化为SOA的研究进展。最后,对实验室模拟SOA形成机制及化学成分研究的不足提出展望。     

大气气溶胶和臭氧浓度垂直分布

本文总结了1984～1994年期间6次平流层气球探测的大气气溶胶和臭氧浓度的垂直分布.垂直分布图中显示了气溶胶和臭氧的浓度在对流层中出现浓度峰,臭氧浓度还在对流层顶附近出现次峰.为了分析这些浓度峰的成因,计算了位温、位涡、后向轨迹,查阅了天气图.主要结果如下(1)对流层大气气溶胶和臭氧的垂直分布受大气稳定度、空气湿度和对流层顶折叠等因子影响;(2)大气气溶胶浓度峰对应臭氧的浓度谷和一个气溶胶浓度低值对应臭氧的高值;(3)对流层气溶胶的柱浓度在1984年8月23日、1993年8月22日、1993年9月12日和1994年9月15日分别是72.2,20.2,20.7和34.4×105/cm2,而0～30 km大气柱的气溶胶浓度在1984年8月23日、1993年8月22日和9月12日分别是89.1,33.1和34.3×105/cm2;(4)0～30 km大气臭氧的积分浓度在1984年8月23日、1993年9月12日为274 DU,271.6 DU,对流层臭氧浓度在1984年8月23日、1993年9月12日和1994年9月15日分别是84.3,60.9和67.5 DU.     

气象条件对北京北郊冬季气溶胶污染的影响

对2004年1月1～12日北京大气物理所气象观测塔院内气溶胶浓度的观测资料和同期的气象资料进行了分析,结果表明北京冬季出现气溶胶污染的频率较高,采样期间超标率达58%,超标发生时地面风速较小,以偏东风为主,并伴有强的低空逆温;稳定性降雪过程对PM10有滞后的清除作用.气溶胶浓度与相对湿度和风速二元线性回归分析结果表明,平均风速对PM10日均浓度的影响较大,北京冬季PM10体现了细粒子的特征.天气形势对气溶胶浓度的影响显著,冬季当北京位于高压或两高压的均压场内,会出现地面高污染.     

东亚地区春季有机碳气溶胶分布特征的初步研究

本研究利用一个区域三维化学输送模式模拟研究了东亚地区2001年春季有机碳气溶胶的输送与演变过程.有机碳气溶胶浓度的模拟值与TRACE-P和ACE-Asia观测期间获取的观测值相比,模拟值与观测值之间具有非常好的一致性,模式合理地反映了有机碳气溶胶浓度的时空分布.模拟结果表明,有机碳气溶胶柱含量的高值区(大于16 mg/m2)主要集中在长江中游和西南地区,黄河以南的我国大部分地区柱含量超过了7 mg/m2,并且4 mg/m2的等值线延伸到了西北太平洋深处.     

Aerosol Precipitation

Abstract

The efficiency of a single-stage wet electroprecipitator was investigated. This separation process is based on ionization of the particles in the first step. The precipitation electrode is formed by the scrubbing liquid. The operating voltage is limited to 20 kV.     

Inverting High Spectral Resolution Aerosol Optical Depth to Determine the Size Distribution of Atmospheric Aerosol

Measurements of aerosol optical depth are presented in the spectral interval 0.40–1.10 μm, which includes the most transparent region of the solar spectrum and the near infrared. The measurements were obtained by a grating spectrometer with a resolution ≈ 0.5 nm during the 1994 summer season at a mountain site (about 850 m above sea level) in the South of Italy. Spectral regions free from gas absorption features have been singled out and used to retrieve the aerosol columnar size distribution. Inversions have been performed by using the Phillips-Twomey inversion method along with a χ² criterion which allows one to choose a suitable value for the regularization parameter. The result of the inversions are presented in the particle radius range 0.1 ÷ 3 μm and indicate the presence of a bimodal aerosol with the second mode radius at about 1.0 μm undergoing transformations which are well correlated with relative humidity.     

Thermophoresis of Aerosol Spheroids

An analytical study is presented for the thermophoretic motion of a freely suspended aerosol spheroid in a uniform prescribed temperature gradient that is oriented arbitrarily with respect to its axis of revolution. The Knudsen number is assumed to be small so that the fluid flow is described by a continuum model with a thermal slip at the particle surface. In the limit of small Peclet and Reynolds numbers, the appropriate energy and momentum equations are solved in the quasisteady situation using the bifocal-coordinate transformations. Explicit expressions for the thermophoretic velocity and force are obtained for various cases of prolate and oblate spheroidal particles. The average thermophoretic velocity and force for an ensemble of identical, noninteracting spheroids with random orientation distribution are also determined. The results indicate that the shape and relative thermal conductivity of a spheroidal particle and its orientation with the thermal gradient can have significant effects on its thermophoretic behavior.     

Size-Fractionating Aerosol Generator

An aerosol generator has been developed and evaluated for applications where the aerosol concentration and size distribution need to be tailored to specific needs. In this device, a modified Wright nebulizer generates the primary aerosol whose concentration and, to a limited degree, size distribution are adjusted through selection of the pressure drop and the gas-to-liquid flow rate ratio. Further modification of the size distribution is achieved through virtual and solid-plate impaction so that specific aerosol concentration in specific size ranges can be chosen as the aerosol output.     

Aerosol Jet Etching

A new etching technology, termed aerosol jet etching (AJE), has been successfully demonstrated and investigated to determine its suitability for microelectronics applications. This technology combines the excellent selectivity of wet chemical etching, the anisotropy of dry etching techniques, and low chemical usage. Experimental results and theoretical interpretations are given for patterned hydrofluoric acid etching of silicon dioxide layers on silicon. The effects of various operating parameters on etch rate, etched surface morphology, side wall profile, and anisotropy are described. These results are used to propose optimum operating conditions for AJE. Also, some unusual surface structures formed under certain conditions during AJE are-described.     

Aerosol Deposition in the Extrathoracic Region

The extrathoracic region, including the nasal and oral passages, pharynx, and larynx, is the entrance to the human respiratory tract and the first line of defense against inhaled air pollutants. Estimates of regional deposition in the thoracic region are based on data obtained with human volunteers, and that data showed great variability in the magnitude of deposition under similar experimental conditions. In the past decade, studies with physical casts and computational fluid dynamic simulation have improved upon the understanding of deposition mechanisms and have shown some association of aerosol deposition with airway geometry. This information has been analyzed to improve deposition equations, which incorporate characteristic airway dimensions to address intersubject variability of deposition during nasal breathing. Deposition in the nasal and oral airways is dominated by the inertial mechanism for particles >0.5 w m and by the diffusion mechanism for particles <0.5 w m. Deposition data from adult and child nasal airway casts with detailed geometric data can be expressed as E n = 1 m exp( m 110 Stk), where the Stokes number is a function of the aerodynamic diameter ( d a ), flow rate ( Q ), and the characteristic nasal airway dimension, the minimum cross-sectional area ( A min ). In vivo data for each human volunteer follow the equation when the appropriate value of A min is used. For the diffusion deposition, in vivo deposition data for ultrafine particles and in vivo and cast data for radon progeny were used to derive the following deposition: E n = 1 m exp( m 0.355 S f 4.14 D 0.5 Q m 0.28 ), where S f is the normalized surface area in the turbinate region of the nasal airway, and D is the diffusion coefficient. The constant is not significantly different for inspiratory deposition than for expiratory deposition. By using the appropriate characteristic dimension, S f , one can predict the variability of in vivo nasal deposition fairly well. Similar equations for impaction and diffusion deposition were obtained for deposition during oral breathing. However, the equations did not include airway dimensions for intersubject variability, because the data set did not have airway dimension measurements. Further studies with characteristic airway dimensions for oral deposition are needed. These equations could be used in lung deposition models to improve estimates of extrathoracic deposition and intersubject variability.